Why does the STM8L external interrupt operate in an endless loop?

　　The STM8L series MCU is a low-power MCU launched by ST. Compared with the STM8S series, the power consumption is much lower, but the internal structure is also much reduced. Be sure to read the manual carefully when using it. This is the first time I use STM8. Since the functions are not very complicated, I did not want to study the library functions. I was ready to directly control the register operation. I didn't expect that I would be entangled in the interrupt problem for most of the day.

This is very different in external interrupts. STM8S automatically clears external interrupts, while STM8L requires software to clear them. The register that clears the flag bit varies depending on the setting, as explained below.

 

The following takes the STM8L external interrupt PB1 as an example to illustrate the operation of the external interrupt register

There are several steps to set up external interrupts:

The first step is to set the IO port as interrupt input by setting (PB_DDR = 0X00; PB_CR1 = 0X02; PB_CR2 = 0X02;)

Step 2: Set the interrupt trigger mode (00: Falling edge and low level; 01: Rising edge only; 10: Falling edge only; 11: Rising and falling edge)

Step 3: Change the interrupt vector table (in the stm8_interrupt_vector.c file)

Step 4: Write an interrupt handling function and remember to clear the interrupt in the function

 

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 Step 1: Set the IO port as interrupt input

   PB_DDR = 0X00; // Input

　PB_CR1 = 0X02; // 0_0010  

　PB_CR2 = 0X02; // 0_0010 CR1 and CR2 are combined to determine the pull-up external interrupt input

Step 2: Set the interrupt trigger mode. The PB and PD ports in STM8L are special and can have two trigger modes.

　EXTI_CONF = 0x00;

  These two trigger modes are set through the register EXTI_CONF 

  The first method is the same as port A and C. The trigger mode is set by the following two registers. Set register EXTI_CONF[0] to 0, indicating that port B[3:0] uses the first method (which I call the normal method here).

　　EXTI_CR1 register sets the 3, 2, 1, 0 pins of Port A, B, C and/or D external interrupts

　　EXTI_CR2 register sets the 7, 6, 5, 4 pins of Port A, B, C and/or D external interrupts

  The second method is to set the trigger mode EXTI_CONF[0] to 1 through the EXTI_CR3 register, indicating that Port B[3:0] uses the second method (I named it the special method here)

　　Bits [3:2] of the EXTI_CR3 register set the trigger mode of port D. 

　　Bits [1:0] of the EXTI_CR3 register set the trigger mode of port B.

Step 3: Change the interrupt vector table 

　　{0x82, KEY_Interrupt}, /* irq9 */

　　The PB1 normal mode interrupt vector number is 9, where KEY_Interrupt can be named according to actual needs as long as it is consistent with the interrupt function name written later.

　　Why choose 9? Look at the picture below to know.

Step 4: Write an interrupt handling function

　　@far @interrupt void KEY_Interrupt(void)
　　{
　　　　LED1 = !LED1;
　　　　//EXTI_SR2 = 0x01; // If set to special mode, clear the interrupt flag through this register
　　　　EXTI_SR1 =0x02; // If set to normal mode, clear the interrupt flag through this register

　　} 

There are two points to note in this step:

1. If the interrupt execution function does not want to be written in the stm8_interrupt_vector.c file, you need to add such a function in the stm8_interrupt_vector.c file

　　@far @interrupt void KEY_Interrupt(void);

2. EXTI_SR2 = 0x01; // If set to special mode, clear the interrupt flag through this register
　　EXTI_SR1 = 0x02; // If set to normal mode, clear the interrupt flag through this register

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Interrupt vector level: 

From the first table below, we can see that if we use normal interrupt mode, the interrupt of port B1 belongs to EXTI1 (if it is PB2, it belongs to EXTI2), and the interrupt of special mode port B belongs to EXTIB and EXTID,

 

 

After knowing this, we can combine it with the interrupt vector table in the manual to know where we should write the interrupt entry function name.